1. Field of the Invention
The present invention relates to an ink jet recording apparatus wherein an ink tank for supplying ink to a recording head is placed over a movable carriage.
2. Description of the Related Art
A structure for supplying ink to a recording head has heretofore been proposed for an ink jet recording apparatus in various ways.
For example, Japanese Published Examined Patent Application No. Sho 54-31898 (hereinafter called xe2x80x9cprior art example 1xe2x80x9d) discloses a structure wherein a liquid storage of a print head is charged with a liquid absorption material and a charging opening fit with a liquid charging device is provided and brought into contact with a wick provided in the liquid charging device, whereby liquid is supplied to the print head by a capillary force.
Japanese Published Examined Patent Application No. Sho 63-51868 (hereinafter called xe2x80x9cprior art example 2xe2x80x9d) also discloses a structure wherein a supply pipe connects between a sub tank mounted to a carriage and a main ink tank provided outside the carriage, and when ink in the sub tank is reduced, the main ink tank is pressed to feed the ink to within the sub tank under pressure, whereby air in the sub tank is stored in a bag-like container through an exhaust pipe.
Further, Japanese Published Examined Patent Application No. Hei 7-51356 (hereinafter called xe2x80x9cprior art example 3xe2x80x9d) discloses a structure wherein a first tank placed over a carriage and a second tank provided outside the carriage are connected to each other by two connecting pipes corresponding to first and second connecting pipes to feed ink from the second tank to the first tank under pressure, and overflowing ink is withdrawn into the second tank. Incidentally, pressure maintenance is effected on a nozzle orifice by pressure applied at this time.
Furthermore, Japanese Published Examined Patent Application No. 2772014 (hereinafter called xe2x80x9cprior art example 4xe2x80x9d) discloses a structure wherein when a remaining-amount-of-ink detection electrode of a first ink tank placed on a carriage detects a reduction in the remaining amount of ink, a mechanical valve of a tube connecting the first ink tank and a second ink tank is opened, so that ink is automatically resupplied from the second ink tank located at a position higher than that of the first ink tank.
Still further, Japanese Published Examined Patent Application No. 2929804 (hereinafter called xe2x80x9cprior art example 5xe2x80x9d) discloses a structure wherein in an ink supply mechanism configured so as to allow separation between a head cartridge unit and an ink cartridge unit, the head cartridge unit has a first chamber having an opening defined therein for communication with air and a second chamber in communication with the first chamber and having a porous member, and is joined with the ink cartridge unit by two or more communication paths having a height difference within the first chamber, whereby ink is supplied from the ink cartridge unit according to differential pressure based on the height difference.
Still further, Japanese Published Unexamined Patent Application No. Hei 4-10946 (hereinafter called xe2x80x9cprior art example 6xe2x80x9d) discloses a structure provided with a pump mechanism in which a first ink tank communicating with a nozzle of a ink jet printer and a second ink tank communicating with the first ink tank are both placed on a carriage and which has a piston idly movable in a reciprocating direction according to the inertia incident to reciprocation motion of the carriage and performs the transfer of ink between the first ink tank and the second ink tank according to the actuation of the piston.
Japanese Published Unexamined Patent Application No. Hei 5-57902 (hereinafter called xe2x80x9cprior art example 7xe2x80x9d) discloses a structure wherein an ink jet head cartridge is provided in which a recording head and an ink storage unit are integrally formed, an ink re-filling cartridge filled with replenishing ink is connected to the head cartridge, and the recording head is sucked under negative pressure to thereby replenish the head cartridge with the ink in the ink re-filling cartridge.
Japanese Published Unexamined Patent Application No. Hei 5-177844 (hereinafter called xe2x80x9cprior art example 8xe2x80x9d) discloses a structure wherein an ink flight unit is provided integrally with an ink cartridge detachably mounted to a cartridge, an ink spare cartridge for refilling the ink cartridge with ink is removably provided, and the junction between the ink cartridge and the ink spare cartridge is made by capillary or tubing.
Japanese Published Unexamined Patent Application No. Hei 7-17046 (hereinafter called xe2x80x9cprior art example 9xe2x80x9d) discloses a structure wherein a print head, an ink tank for replenishing ink, and a pump for delivering ink from the replenishing ink tank are mounted on a carriage, and the pump is actuated based on a signal detected by a remaining-of-amount-of-ink detector attached to the print head to supply the ink.
In Japanese Published Unexamined Patent Application No. Hei 9-187967 (corresponding to U.S. Pat. No. 5,815,172)(hereinafter called xe2x80x9cprior art example 10xe2x80x9d) and Japanese Published Unexamined Patent Application No. Hei 10-128992 (hereinafter called xe2x80x9cprior art example 11xe2x80x9d), a structure is disclosed wherein a print cartridge replaceable with a cartridge is placed and connected to an ink supply unit placed within a printer through an ink tube. Further, a structure is disclosed wherein a pump chamber for pressurizing an ink supply unit is provided and a print cartridge is provided with a pressure control valve, whereby ink is supplied to a print head under suitable negative pressure.
U.S. Pat. No. 5,912,687 (hereinafter called xe2x80x9cprior art example 12xe2x80x9d) discloses a structure wherein a nozzle for replenishing ink is elongated and joined to a print head placed on a carriage to supply pressurized ink from an in ink cartridge.
Japanese Patent Unexamined Patent Application No. Hei 10-29318 (hereinafter called xe2x80x9cprior art example 13xe2x80x9d) discloses a method of replenishing a liquid storage container having a first chamber holding a negative pressure generating member therein and having an opening in communication with the outside, and a second chamber which communicates with the first chamber through a communication portion and defines a hermetically sealed space, with liquid by using a replenishing container, i.e., a structure wherein gas in the second chamber and gas in the replenishing container, and liquid in the second chamber and liquid in the replenishing container are allowed to communicate with one another through different paths respectively. This discloses that the pressure of the gas in the second chamber and the pressure of the gas in the replenishing container are balanced by causing the gases to communicate with each other in this way, and the liquids are respectively supplied so as to reach a predetermined liquid surface or level by the difference in head pressure.
Incidentally, one example in which an ink chamber for supplying ink to a recording head is brought to a predetermined vacuum state, has been disclosed in Japanese Published Unexamined Patent Application No. Hei 7-81084. Namely, this discloses that a sub-ink chamber for holding an ink absorption member communicates with a main ink chamber through a meniscus formation member having a small hole defined therein and thereby ink is supplied from the ink absorption member to the main ink chamber through the meniscus formation member when negative pressure increases with the consumption of ink in the main ink chamber, thereby maintaining the negative pressure. This also discloses that after all the ink in the ink absorption member are used up, a suitable amount of air (bubbles) is supplied through an ink meniscus film formed on the meniscus formation member to thereby keep the negative pressure of the main ink chamber constant.
The respective prior art examples involving the following inconveniences.
The prior art example 1 has the inconvenience that the satisfactory transfer of ink is not performed depending on the condition of a distribution of liquid in the liquid storage, and since the wick is always exposed, the liquid is apt to cause evaporation and modification.
The prior art example 2 has the inconvenience that the sub tank is brought to positive pressure upon feeding of the ink under pressure and the positive pressure acts on an orifice of a recording head, thereby causing the leakage of the ink.
The prior art example 3 has the inconvenience that the first tank is required to be placed below a head and the ink is apt to leak from the connected portion by the pressure maintenance.
The prior art example 4 has the inconvenience that when the mechanical valve is deteriorated, the ink leaks.
The prior art example 5 has the risk of causing the leakage of ink from the air communication hole because the first chamber is open to air, when the position of the head cartridge unit is changed.
The prior art example 6 is accompanied by a problem that is actually difficult to fabricate a piston pump idly movable by the reciprocation of the carriage (very small in operating resistance), and even if it is possible to fabricate the piston pump, it is brought to a complex mechanism, thus causing an increase in cost.
The prior art example 7 is accompanied by a problem that the recording head needs to be subjected to a vacuum state and the ink absorbed from the recording head at this time results in useless waste ink. A problem also arises in that the amount of ink with which the head cartridge can be refilled, cannot be controlled accurately.
The prior art example 8 is accompanied by a problem that while a sponge is placed within the ink cartridge as a member for supplying suitable negative pressure to a head, the pressure supplied to the head will change because the amount of ink stored in the sponge changes according to the amount of ink re-supplied from the ink spare cartridge. Also a problem arises in that when the coupling between the capillary or tubing and the sponge by fluid is rendered unstable even a bit, the simple absorption of air from an air communication hole makes is impossible to use the ink in the ink spare cartridge.
The prior art example 9 is accompanied by a problem that since the pump is required between the print head and the ink tank, an apparatus scales up and increases in cost. It has the inconvenience that the weight of the carriage also increases.
The prior art examples 10 and 11 are respectively accompanied by a problem that since the pressure pump chamber for the ink tube and the ink supply unit, the pressure control valve for the print cartridge, etc. are so complicated in system, they increase in cost for their implementation and an apparatus increases in size.
According to the prior art example 12, there is a fear of the leakage of ink from a connecting portion because the ink is supplied by pressurization. It is also necessary to accurately control the amount of ink to be replenished.
In the prior art example 13, the position of placement of the replenishing container is restricted because it is necessary to provide a mechanism for allowing the liquids and gases in the first and second chambers to always communicate with one another. It is also necessary to provide a long gas communication pipe for the purpose of allowing the gases to communicate with each other. Further, difficulties are encountered in fabricating and placing such a communication pipe, and irregular ink enters into the long gas communication hole. As a result, a problem arises in that ink""s meniscus interferes with the balance in pressure between the gases and no ink is replenished from the replenishing container.
The present invention has been made to solve the inconveniences and provides an ink jet recording apparatus which is compact in structure and replenishes a suitable amount of ink.
According to one aspect of the present invention, there is provided an ink jet recording apparatus including a main ink tank which is placed over a movable carriage provided with a print recording head and has a first ink chamber which holds ink supplied to the recording head therein in a state having a free surface, a sub-ink tank having a sub-ink chamber with ink held therein, and at least one connecting unit having at least one communication path which allows the first ink chamber and the sub-ink chamber to communicate with each other, and wherein air in the first ink chamber and the ink in the sub-ink chamber are interchanged with each other through the communication path according to a change in pressure in the first ink chamber, which is developed by acceleration or deceleration based on scanning of the movable carriage, whereby the ink is supplied from the sub-ink tank to the main ink tank.
When the movable carriage is scanned upon printing, a force proportional to the mass of ink acts on the ink held in the main ink tank to thereby change pressure applied to the ink in the main ink tank. The change in pressure swings a free surface of ink and produces an irregular pressure distribution developed by the swing of the ink""s free surface, within the main ink tank.
When, at this time, pressure acts even on the communication path (interface between air and ink) between the main ink tank and the sub-ink tank and thereby the pressure in the main ink tank relatively increases, air stored above the main tank is discharged into the sub-ink tank. When the pressure in the sub-ink tank rises in reverse, ink placed below the sub-ink tank is discharged into the main ink tank. Owing to the repetition of such action according to the scanning of the carriage, the air stored in the main ink tank ad the ink in the sub-ink tank are interchanged with each other.
Namely, the ink is supplied from the sub-ink tank to the main ink tank by the printing operation to compensate for the consumption of ink in the first ink chamber by printing. Accordingly, a special driving unit or the like for the supply of ink is not required and thereby the present apparatus can be simplified in structure.
According to another aspect of the present invention, there is provided an ink jet recording apparatus wherein the connecting unit has plural communication paths, and the air in the first ink chamber and the ink in the sub-ink chamber are interchanged with each other according to a difference or differential pressure between respective head pressures developed in the plural communication paths to thereby supply the ink from the sub-ink tank to the main ink tank.
Plural communication paths for allowing the sub-ink chamber and the first ink chamber to communicate with each other are provided and a differential pressure is developed between ink""s head pressures developed in the communication paths.
Since, at this time, the differential pressure is applied to the change in pressure developed by the scanning (acceleration) of the carriage, the air in the main ink tank and the ink in the sub-ink tank can be exchanged smoother with one another.
Thus, the ink can be supplied from the sub-ink tank to the main ink tank with more reliability without a special supply unit owing to the provision of the plural communication paths and the use of the deferential pressure between their head pressures.
According to a further aspect of the present invention, there is provided an ink jet recording apparatus wherein the plural communication paths have height differences at open ends in the first ink chamber.
By allowing the plural communication paths to have the height differences at the open ends in the first ink chamber, the difference or differential pressure occurs between the respective head pressures developed in the plural communication paths.
Thus, the ink can be supplied from the sub-ink tank to the main ink tank according to the developed differential pressure.
According to a still further aspect of the present invention, there is provided an ink jet recording apparatus wherein the sub-ink tank is placed over the movable carriage and detachably mounted to the main ink tank.
Since the sub-ink tank is also placed over the movable carriage and detachably mounted to the main ink tank, the sub-ink tank is replaced with another when the remaining amount of ink in the first ink chamber is reduced, whereby the main ink tank can be used continuously. Accordingly, the recording head formed integrally with the main ink tank can be utilized until it is put out of action.
According to a still further aspect of the present invention, there is provided an ink jet recording apparatus wherein the main ink tank has a negative pressure control unit which controls the first ink chamber for supplying ink to the print recording head to a predetermined vacuum state.
Since the first ink chamber is controlled to the predetermined vacuum state by the negative pressure control unit, it is possible to restrain or control an increase in negative pressure in the first ink chamber due to the consumption of ink and reliably prevent the occurrence of leakage of ink due to the action of positive pressure on the recording head. Accordingly, satisfactory printing is made possible.
According to a still further aspect of the present invention, there is provided an ink jet recording apparatus wherein the negative pressure control unit includes a second ink chamber which absorbs the ink in the first ink chamber, corresponding to expansion of air in the first ink chamber and sub-ink chamber at a change in ambient environment while the vacuum state is being kept.
The ink jet recording apparatus has the fear of expanding the air in the first ink chamber and sub-ink chamber due to the change in ambient environment, e.g., a rise in ambient temperature and thereby reducing the negative pressure in the first ink chamber. The extreme case was that the first ink chamber was brought to the positive pressure to thereby cause the leakage of the ink from the recording head. In the present invention, however, the vacuum state of the first ink chamber can be maintained because the ink in the first ink chamber, corresponding to the expansion of air in the first ink chamber and sub-ink chamber due to the change in ambient environment is absorbed into the second ink chamber by the negative pressure control unit.
According to a still further aspect of the present invention, there is provided an ink jet recording apparatus wherein the negative pressure control unit includes a capillary member for holding ink therein, a second ink chamber which holds the capillary member therein and has an air communication hole, and a meniscus formation member which is placed at a portion where the first ink chamber and the second ink chamber communicate with each other, and forms ink meniscus.
The main ink tank is provided with the second ink chamber, which communicates with the first ink chamber through the meniscus formation member and has the air communication hole. Therefore, when the liquid level of ink in the first ink chamber is lowered by printing, the ink is supplied from the capillary member of the second ink chamber to the first ink chamber through the meniscus formation member owing to increased negative pressure of the first ink chamber, whereby the vacuum state of the first ink chamber can be maintained at a suitable level. When the negative pressure of the first ink chamber increases after the ink in the second ink chamber is fully used up (air has reached the meniscus formation member), an ink meniscus film formed on the meniscus formation member is broken to supply bubbles (air) from the second ink chamber to the first ink chamber, whereby the negative pressure of the first ink chamber is controlled to a predetermined range. Further, when the pressure of the first ink chamber increases due to the change in ambient environment, the ink is absorbed into the interior of the capillary member of the second ink chamber through the meniscus formation member, thereby making it possible to maintain the negative pressure within the predetermined range.
According to a still further aspect of the present invention, there is provided an ink jet recording apparatus wherein a negative-pressure maintainable capacity of the second ink chamber is defined as Xm1 and the amount of expansion of the air in each of the first ink chamber and the sub-ink chamber at the change in ambient environment is defined as Ym1, both satisfy the relations in X≳Y.
If the negative-pressure maintainable capacity of the second ink chamber, e.g., an ink absorbable capacity of the capillary member is set so as to be greater than the expansion of air in each of the first ink chamber and sub-ink chamber due to the change in ambient environment, then a change in the negative pressure of the first ink chamber can reliably be controlled to a predetermined range and hence satisfactory printing can be ensured.
According to a still further aspect of the present invention, there is provided an ink jet recording apparatus further including a ink-remaining-amount detecting unit which detects the remaining amount of ink in the first ink chamber.
In the ink jet recording apparatus according to the present invention, the ink in the sub-ink chamber is used up antecedent to the ink in the first ink chamber by printing. Thus, if the remaining amount of ink in the first ink chamber is less than or equal to a predetermined amount, then the ink-remaining-amount detecting unit is capable of assuredly detecting the absence of the remaining amount of ink in the sub-ink chamber. Accordingly, the sub-ink tank attached to the main ink tank is replaced with another based on the detected remaining amount of ink. This exchange can be carried out with suitable timing.
According to a still further aspect of the present invention, there is provided an ink jet recording apparatus wherein the ink-remaining-amount detecting unit optically detects a liquid level of the ink in the first ink chamber.
Since the ink-remaining-amount detecting unit optically detects the liquid level of the ink in the first ink chamber, the first ink chamber needs not to provide a special member thereinside and hence the present apparatus becomes simple in structure.
According to a still further aspect of the present invention, there is provided an ink jet recording apparatus wherein the ink-remaining-amount detecting unit applies light to the first ink chamber and detects a liquid level of ink therein from an attenuation factor of the light.
The ink-remaining-amount detecting unit applies the light to the first ink chamber and makes a decision as to the presence or absence of ink at a light-applied position based on the attenuation factor of the reflected light. Thus, the remaining amount of ink in the first ink chamber can be detected with satisfactory accuracy. Further, unsuitable ink can be detected by finely setting the attenuation factor. Thus when the unsuitable ink is detected, the present detecting unit may be configured so as to encourage the exchange of the sub-ink tank, main ink tank and recording head.
According to a still further aspect of the present invention, there is provided an ink jet recording apparatus wherein the connecting unit includes at least one pipe mounted to the main ink tank and having one end open within the first ink chamber and the other end provided with a transverse hole, a cover member which is mounted to the main ink tank and which hermetically seals the pipe from the outside and exposes the other end of the pipe to the outside by the action of an external force, and a seal member which is provided in the sub-ink tank and which hermetically seals the sub-ink chamber from the outside and allows the exposed pipe to hermetically enter the sub-ink chamber when the sub-ink tank is pressed toward the main ink tank.
When no sub-ink tank is mounted to the main ink tank, the pipe of the main ink tank is hermetically sealed from the outside with the cover member. Therefore, the vacuum state of the first ink chamber is maintained and the ink is prevented from evaporating through the pipe. Further, since the sub-ink tank is also hermetically sealed with the seal member, no ink leaks from the sub-ink chamber.
Owing to the attachment of the sub-ink tank to the main ink tank in this condition, the cover member pressed to the sub-ink tank exposes the pipe to the outside and allows the other end (lateral hole) of the pipe to enter into the sub-ink tank. Thus, the first ink chamber and the sub-ink chamber are capable of communicating with each other in a hermetic (fluid-tight) state.
According to a still further aspect of the present invention, there is provided an ink jet recording apparatus including a main ink tank which is placed over a movable carriage provided with a print recording head and has a first ink chamber which holds ink supplied to the recording head therein in a state having a free surface, a sub-ink tank having a sub-ink chamber with ink held therein, and at least one connecting unit having plural communication paths which allow the first ink chamber and the sub-ink chamber to communicate with each other, and wherein air in the first ink chamber and the ink in the sub-ink chamber are interchanged with each other according to a differential pressure between respective head pressures developed in the plural communication paths of the connecting unit, whereby the ink is supplied from the sub-ink tank to the main ink tank.
The sub-ink chamber and the first ink chamber are connected to each other by the connecting unit through the plural communication paths, and the ink can be supplied from the sub-ink chamber to the first ink chamber according to the differential pressure between the head pressures developed in the plural communication paths.
Thus, the use of the differential pressure between the head pressures makes it possible to supply the ink from the sub-ink tank to the main ink tank without having to use a special ink supply unit.